Study On The Behaviour Of Mass Concrete Under Complex Stress State With Tests And Numerical Modeling

In practical engineering, most concrete buildings, especially hydraulic mass concrete structure, such as various gravity dams and arch dams, are generally working under biaxial or triaxial stress state. At present, a great deal of experimental research on the deformation and strength of the common small aggregate concrete has been carried out, but the biaxial and triaxial experiments on strength and deformation of mass concrete, which are commonly used in hydraulic engineering are seldom done at home and abroad, except a few biaxial tension-compression experiments on fully-graded concrete carried out in DLUT. In this paper, the strength and deformation characteristics of hydraulic mass concrete and wet-screened concrete under complex stress state are compared on the basis of experiments; the failure processing and its macro-mechanical responsive features are studied by means of numerical simulation. The major contributions are summarized as follows:(1) Tests on uniaxial compression and tension of three-graded concrete and wet-screened two-graded concrete are carried out. A series of experience formulas, which reflect the relations among compressive strength, tensile strength, peak strains, and elastic modulus, are obtained by means of regressive analysis on a great amount of domestic and overseas uniaxial test data of dam concrete. This can be referred to in engineering practice. The growth law of damage and propagation of micro-cracks in various sized concrete specimens under uniaxial loading are investigated with ultrasonic pulse measurements. Then the effects of aggregate size, aggregate volume content and specimen size on the damage evolution of concrete are studied.(2)The behavior of deformation and strength of the three-graded concrete and the corresponding wet-screened two-graded concrete under biaxial compression-tension and triaxial compression-compression-tension stress states is studied experimentally. Test methods and test programs as well as the test condition and loading devices demanding are explored for biaixal compression-tension and triaxial compression-compression-tension tests of the mass concrete. By regression of the tests results, respective failure criterions for mass concrete in principal stress space and octahedronal stress space are proposed.(3)Experimental study on the deformation and strength of various aggregate grading and sized concrete specimens under biaxial compression is carded out. Two cases of loading types are adopted: one is biaxial proportional loading and the other is axial loading with one-side constant confining pressure. The strength, deformation and crack pattern of different aggregate-graded concrete under different loading paths are analyzed systematically. Failure criterion of different graded concrete under biaxial compression is established both in normal stress space and in normal strain space.(4)Based on the fundamental test data and the mesoscopic approach in which the concrete is treated as a three-phase inhomogeneous system, a rigid body spring model is developed for simulation of the behaviour of large aggregate concrete subjected to uniaxial or multiaxial load. The comparison of numerical and experimental results shows this method could effectively describe the failure behaviour of concrete under various plane stress state.(5)Combined endochronic theory developed by Valanis with the revised damage theory developed by Mazes, a new endochronic damage constitutive model suitable for various aggregate graded concrete is proposed. This model takes the scale effect and the effect of wet screen sieve of aggregate into consideration in which the concept of yield surface is not needed and the difference of damage evolution rule of various graded aggregate concrete is to be concerned.